1. Learning Outcomes:
Determine the order of reaction using:
(i)
Initial rate method
Initial rate method Example 1:
O2(g) +
Exp
1
2
3
4
5
2NO(g)
2NO2(g)
Initial concentrations(molL-1)
O2
NO
-2
1.10 x 10
1.30 x 10-2
2.20 x 10-2
1.30 x 10-2
1.10 x 10-2
2.60 x 10-2
3.30 x 10-2
1.30 x 10-2
1.10 x 10-2
3.90 x 10-2
(a) Determine the order of reaction with respect to
(i) O2
(ii) NO
(b) Write the rate law
(c) Determine the overall order of the reaction
Initial rate
(molL-1s-1)
3.21 x 10-3
6.40 x 10-3
12.8 x 10-3
9.60 x 10-3
28.8 x 10-3

2. SOLUTI
ON:
(a)
Step 1: Write the rate law
Let the rate law
Compare experiment 2 with 1

3. Compare experiment 3 with 1
3.98

4. Initial rate method Question 1:
The following of nitric oxide with hydrogen at 12800C is
The following data was collected at this temperature :
Exp
1
2
3
Initial concentrations(M)
NO
H2
-3
5.00 x 10
2.00 x 10-3
10.00 x 10-3
2.00 x 10-3
10.00 x 10-3
4.00 x 10-3
Initial rate (Ms-1)
1.25 x 10-5
5.00 x 10-5
10.00 x 10-5
Based on the data above, determine
(a) rate law
(b) rate constant
(c) overall order of reaction
(Answer: 2.5 x 102M-2s-1)
TIPS: must write the unit

5. Initial rate method Question 2:
The data below were obtained from the following reaction at 27 oC
Exp
NaOH
1
2
3
Initial concentrations(M)
Reaction rate
(M min-1)
0.25
0.50
0.25
3.0 x 10-3
6.0 x 10-3
9.0 x 10-3
0.15
0.15
0.45
(a) What is the order with respect to each reactant?
(b) Write the rate equation

6. Initial rate method Chalenging Question 1:
Exp
1
2
3
4
Initial concentrations(moldm-3)
X
Y
0.01
0.01
0.01
0.02
0.02
0.01
0.02
0.03
(a) State the order of reaction with respect to
(i)
X
(ii)
Y
(b) State the overall order of reaction
(c) Calculate the rate constant, k and state its unit
(d) Determine the value of s
Initial rate (mol
dm-3min-1)
1.5 x 10-2
3.0 x 10-2
6.0 x 10-2
s

7. Initial rate method Question 3:
Exp
1
2
3
4
5
6
Initial concentrations(mol dm-3)
H2
NO
-3
1.0 x 10
6.0 x 10-3
2.0 x 10-3
6.0 x 10-3
3.0 x 10-3
6.0 x 10-3
6.0 x 10-3
1.0 x 10-3
6.0 x 10-3
2.0 x 10-3
6.0 x 10-3
3.0 x 10-3
(a) Determine how the rate of reaction is affected by,
(i)
Concentration of H2
(ii)
Concentration of NO
(b) Write the rate equation for the reaction
(c) State the overall order of reaction
(d) Calculate the value of the rate constant, k
Initial rate (mol
dm-3s-1)
3.0 x 10-3
6.0 x 10-3
9.0 x 10-3
0.5 x 10-3
2.0 x 10-3
4.5 x 10-3

8. Initial rate method Question 4:
The data for the initial rates of disappearance of
Exp
1
2
3
4
](M)
0.164
0.164
0.082
0.246
are given below
(M)
0.15
0.45
0.45
0.15
Initial rate (Ms-1)
3.2 x 10-5
2.9 x 10-4
1.4 x 10-4
4.8 x 10-5
Determine the rate law and the rate constant for this reaction. If the rate of disappearance of
is 2.2 x 10-4Ms-1, what would be the rate of formation of CO2?
[Ans: 4.4 x 10-4]

9. Initial rate method Question 5:
Experiment
[MnO4ˉ]/M
[ClO3ˉ]/M
[H+]/M
1
2
3
4
0.10
0.25
0.10
0.10
0.10
0.10
0.30
0.10
0.10
0.10
0.10
0.20
Determine the rate law and rate constant for the reaction.
Initial Rate/
M sˉ1
5.2 x 10-3
3.3 x 10-2
1.6 x 10-2
7.4 x 10-3
[Ans: 16.4]

10. Initial rate method Question 6:
TABLE 1 shows the results obtain from the reaction
aX +
bY
cZ
at a specific temperature.
Experiment
1
2
3
4
Initial
X
Y
concentration (M)
1.0
1.0
2.0
2.0
1.0
3.0
3.0
2.0
Initial rate of formation
of Z
2.20 x 10-4
-1
(M x 10)
1.70min -3
6.60 x 10-4
3.96 x 10-3
Write the rate differential equation for the above reaction. What is the order of reaction with respect to
X and Y? Calculate the rate constant, k for the reaction.
[Ans:Rate constant, k = 2.2 10-4 M-2 min-1]

11. Initial rate method Chalenging Question 2 :
The reaction between C and D is represented as follows:
The experiment results are shown in the table below:
Exp
1
2
3
Initial concentrations(M)
C
D
0.10
0.10
0.05
1.00
2.00
1.00
Time
interval
(min)
30
30
120
The change
in
concentration
of C (M)
2.5 x 10-3
1.0 x 10-2
5.0 x 10-3
(a) Calculate the rate of reaction for each experiment
(b) Determine the order of reaction with respect to C and D write the rate law
(c) State the effect on the reaction rate if the concentration of D is doubled but the
concentration of C remains constant.